I've got an iPad 4, been using Auria happily for a couple of years. This week was the first time I've worked with Auria on OS 11 (I only use Auria for the mastering stage) and, along with the intermittent disappearance of sound from certain channels, the buffer size function isn't working. Actually, this morning I was able to work with a setting of 2048, but I happened to close it during lunch, and when I re-opened it the buffer size moved to 256.
This, after I wrestled with the same issue yesterday and went through the trouble of starting up a new, empty project and step-by-step recreated the same song with the same settings from scratch. (Auria Pro, if that matters)

This is unfortunately how buffer sizes work on iOS. An app can only "ask" for a certain buffer size, and there's no guarantee that iOS will allow it at a given time. This is because for the most part, the first app that requests a buffer size will receive it. So if you have other apps running, close them first, then open Auria and request the buffer size you need. Also, some apps don't like large buffer sizes, so that may be a limiting factor as well.

So...are you telling me that Auria will never be able to offer its user a stable buffer size? (Btw, I have had some success in getting it to go up to 4096, even, but that was with Gadget having been opened first and also with the iPad unplugged from my Presonus interface)

What I'm talking about is not an Auria only issue, it's an iOS issue. All apps are affected by the same rules. iOS doesn't guarantee buffer sizes to any app. You can ask, but iOS doesn't always give an app what it asks for. That's why I added an indicator next to where you set the buffer size to let you know what buffer size iOS agreed to give Auria.

You made that point clear enough in your initial response. Anyway, because this is kind of important to me, I've been thinking of possible fixes and what just occurred to me is that perhaps there might be some kind of conflict between Auria and another audio/buffer-requiring app. So just now I deleted from my iPad Spotify and a radio app. The thing about my particular case is that this buffer size thing was not a problem in OS10, plus there's the fact that I only installed Spotify between my previous Auria mastering project and this current project.

Thanks for your help, Rim. Auria is only as good an app as the iPad will allow it to be.

Interesting. There might be something that's changed since iOS11 got released, but in any case just having an app installed (like Spotify) shouldn't be making a difference. It only comes into play when the app is actually launched. So I'm not sure why it would make a difference in your case. Have you tried some simple experiments, like restarting your iPad, then double tapping to make sure everything is closed and launching Auria, and setting the buffer to 4096? If Auria is the only app running, it should stay at the buffer size you selected forever.

Also, I assume you're not using MIDI (I should have asked first). iOS doesn't permit buffer sizes larger than 512 if you're using MIDI. For Auria that means if your project contains at least one MIDI track.

Yes, I have tried the obvious and basic things. One "fix" that was working for a while is that I (after a clean reboot) first open Gadget at its highest buffer setting, then I open Auria second. In Auria I then request a larger buffer size (2046/4098 or whatever) and, because sure as shit it wil stay at 256 or 512, I then open a new project. That new project, so far, will show the large buffer size I requested in the previous project. Then I reopen that previous project (the current project) and voilá, I have my desired bufffer setting.
Now, however, after a mix down of one of my stems (one of 4, with a total of ten tracks/channels), which I did to ease the load as much as possible, I attempted to run my mix through Q2's spectrum matching feature (sidechain reference track and all) and it crashed! Also, it currently crashes every time I try to open it (yes, even after a clean reboot).
My first idea is to delete Auria and re-download, build the project from scratch (again). Is that right, or can you suggest something better?

Gadget is a MIDI app. If you have any MIDI capable apps running in your iPad, you won't be able to reliably use a buffer size more than 512. That might be the issue here. Apple just doesn't support it (to be more specific it's CoreMIDI which doesn't support anything higher than 512). You can trick iOS into allowing a higher buffer size, but you'll start getting notes that appear out of time and other strange artifacts, so I wouldn't recommend it. The only way to reliably get higher buffer sizes is to use apps that don't have MIDI.

Happy news: all the buffer problems have gone away! Although I can't fully be certain I have reason to believe it may be because I'm no longer trying to work at the 64bit mixer setting. 32 bit mixing it is from here on out (or at least until I upgrade to an iPad Pro).